In recent years, higher definition CCD/CMOS image sensors have been developed and this requires the improvement in sensitivity of the sensors. Microlenses mounted on such sensors are thus required to have high transparency and high heat resistance.
A known method for producing the microlens for a CCD/CMOS image sensor is an etch back method (Patent Document 1 and Patent Document 2). In the method, a resist pattern is formed on a resin layer for a microlens formed on a color filter layer and the resist pattern is treated with heat to be reflowed, thus affording a lens pattern. The lens pattern formed by reflowing the resist pattern is used as an etching mask and the resin layer for a microlens as the underlayer is subjected to etch back to transfer the lens pattern shape to the resin layer for a microlens, thus yielding a microlens.
In the etch back method, for the accurate transfer of a lens pattern shape to a resin layer for a microlens as the underlayer, a dry etching rate X of the resist and a dry etching rate Y of the resin layer for a microlens are required to be substantially equal (X:Y=1:0.8 to 1.2).